In recent years, much interest has been evidenced in a field now widely known as computed tomography. In a typical procedure utilizing computed tomography (or CT), an X-ray source and detector are physically coupled together on opposite sides of the portion of a sample which is to be examined. The sample may be, for example, a patient or phantom or other objects. X-rays are made to transit through the sample to be examined, while the detector measures the X-rays which make it through the sample without being absorbed or deflected. Periodically, the paired source and detector are rotated to differing angular orientations about the sample, and the data collection process repeated.
A very high number of measurements of attenuation values may be obtained by procedures of this type. The relatively massive amounts of data thus accumulated are processed by a computer, which typically does a mathematical data reduction to obtain attenuation values for a very high number of transmission values (typically in the hundreds of thousands) within the section of the sample being scanned. This data may then be combined to enable reconstruction of a matrix (visual or otherwise) that constitutes an accurate depiction of the density function of the sample section examined.
By considering one or more of such sections, skilled medical diagnosticians may diagnose various body elements such as tumors, blood clots, cysts, hemorrhages and various abnormalities, which, heretofore, were detectable, if at all, only by much more cumbersome and, in many instances, more hazardous techniques to the patient.
While systems of the aforementioned type have represented powerful diagnostic tools, and were deemed great advances in the radiography art, first generation systems suffered from many shortcomings. Acquisition of the raw data frequently entailed an undesirably long period, which, among other things, subjected a patient to both inconvenience and stress. The patient's inability to remain rigid for such a lengthy period, also led to blurring of the image sought to be obtained.
Radiation therapy is another aspect having a great deal of interest. Conventional radiation therapy techniques typically involve directing a radiation beam at a tumor in a patient to deliver a predetermined dose of therapeutic radiation to the tumor according to an established treatment plan. This is typically accomplished using a radiation therapy device.
Tumors have three-dimensional treatment volumes which typically include segments of normal, healthy tissue and organs. Healthy tissue and organs are often in the treatment path of the radiation beam. This complicates treatment, because the healthy tissue and organs must be taken into account when delivering a dose of radiation to the tumor. While there is a need to minimize damage to healthy tissue and organs, there is an equally important need to ensure that the tumor receives an adequately high dose of radiation. Cure rates for many tumors are a sensitive function of the dose they receive. Therefore, it is important to closely match the radiation beam's shape and effects with the shape and volume of the tumor being treated.
In many radiation therapy devices, the treatment beam is projected through a pre-patient collimating device (a “collimator”), which defines the treatment beam profile or the treatment volume at the treatment zone. A number of different collimator techniques have been developed to attempt to conform the dose rate and the treatment volume to the shape of the tumor while taking nearby healthy tissue and organs into account. A first technique is to use a collimator with solid jaw blocks positioned along a path of the treatment beam to create a field shape based on the shape of the tumor to be treated. Typically, two sets of blocks are provided, including two blocks making up a Y-jaw generally disposed parallel to a Y-axis (with the Z-axis being parallel to the beam path), and two blocks making up an X-jaw generally disposed parallel to an X-axis. The X-jaw is conventionally placed between the Y-jaws and the patient.
These solid jaw blocks, however, do not provide sufficient variability in the field shape. In particular, where the tumor has a shape which requires a field edge relatively parallel to the edge of the jaw blocks, the edge of the jaw block becomes more predominant in forming the field edge. As a result, undulation of the field increases as well as the effective penumbra. This can be particularly difficult where the treatment beam is an X-ray beam. It is also difficult to adjust the field shape where the treatment beam is an electron beam due to electron attenuation and scattering.
In a typical radiation therapy device, a frame housing the linear accelerator (X-ray tube) and collimators having a large opening into which the patient is inserted (referred to herein as a gantry) is swiveled around a horizontal axis of rotation in the course of a therapeutic treatment of the patient. The linear accelerator generates a high-energy radiation beam (referred to herein as a “photon beam” or “photons”) for use in the therapeutic treatment.
Historically, linear accelerators used in radiation therapy applications have been equipped to provide only a single energy photon beam. In the recent past, however, some linear accelerators have been equipped to provide two different energy beams. The limited number of energies available is a continuing problem for physicians and physicists, since it is not always possible for them to give the most efficacious treatments. Currently, certain manufacturers are attempting to provide linear accelerators with the capability of generating three different photon energies. Such machines, however, will still preclude much other intermediate energy that may be useful.
A therapeutic x-ray beam produced by a linear accelerator is characterized by the amount of energy that will be deposited at a treatment site by that particular x-ray beam. This characterization relates to the depth (usually measured from the surface of the skin) at which the beam's maximum energy is deposited (often referred to in the art as “dmax”).
Nevertheless, these radiation technologies do not permit the system to be able to perform simultaneous treatment of an area using different types of radiation treatments. Additionally, none of these systems and methods permit computerized tomography to occur during treatment, thereby leading to more accurate treatment of the patient.
Accordingly, it would be beneficial to provide a system that permitted multiple types of radiation therapy to be performed simultaneously. It would also be beneficial to provide a system that was capable of performing radiation therapy with computerized tomography to permit more accurate treatment.